Interesting. I just did another test with two computers, one with a 1000 mbps client PC(A) and another 100mbps server PC (B). B is running iperf3 as server.
So when A starts a iperf3 session in the download direction, i.e. B sending data to A, I get the following:
- no change in ping times when I ping the router (i.e. less than 1 ms)
- Speedtest (done on A) downloads are 100mbps less than max, i.e. I get around 840mbps
- Speedtest (done on A) uploads are at max, i.e. I get around 930mbps
When A starts an iper3 session in the upload direction, i.e. A sending data to B, I get the following:
- Ping time increased to around 16ms
- Speedtest (done on A) downloads are at max, around 930mbps
- Speedtest (done on A) uploads are cut to half, around 470 mbps
I think this looks more like a Linux kernel issue rather than the switch hardware.
The iperf3 runs are both at max for up and down, i.e. 95mbps.